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Widely spread mayfly, body lenght 9 to 13 mm.
Ventral view
Mature nymphs (dark wing-case) are found between April/May
Femura with dark spot
1) Gill 1 crenate. (Gills 2 - 7 entire, without crenation. Not shown in the picture)
2) Gill 1 with plica
2b) Plica with concave front margin